This invention relates to clearing sensors of debris to provide more accurate sensing data. A particular embodiment specifically relates to reducing film buildup over optical sensors in an optical sorting machine due to impurities carried along with the articles to be sorted.
Optical sorting machines, of the type to which an embodiment of this invention relates, work on the principle of light attenuation. Generally, sorters of this type are used to sort articles, such as glass cullet or other material, for post consumer recycling and processing. The glass cutlet are intermixed with dirt, sand, and other impurities; it is not economically viable to preclean the cullet. Although optical sorting of glass is offered as an example, the problems of impurity build-up applies to any sorting machine. For example, metallic build-up on an eddy current sensor can affect its operation. Liquid or particulate build-up on a plastic sorting machine can affect its operation.
Optical sorters of this type generally work as follows. The cullet pass through a sensing field where light of different wavelengths is emitted by light sources and sensed by sensors. The sensors generate signals corresponding to the magnitude of light sensed. Cullet of different color attenuate different wavelengths of light different amounts. This attenuated light signal is compared against a baseline value for the signal to determine the color of the cullet.
Impurities carried along with the cullet buildup over the sensors. This shifts the attenuation value and leads to missorts. These missorts may lead to less pure sorted lots. Lower quality lots are, thus, passed on for subsequent processing. Alternatively, cullet having potential value are erroneously discarded due to shifted attenuation readings.
Prior art has attempted to compensate for impurity, or film, buildup by increasing, or lowering, the baseline value over time. This has proved less than satisfactory. One reason for the short fall is that the impurity layer is not uniform. As the film layer builds, cutlet tend to create furrows in the film layer. This results in nonuniformities in the film layer, and tends to lead to missorts.
The prior art has also attempted to solve the problem by cleaning the screen. However, the cleanser can affect the sort.
The prior art has also attempted to solve the problem by repeatedly replacing the wearcover; this increases expense and down time.
What is needed is a device to reduce light attenuation shifts due to film build up in an optical sorting device. This needed system must be efficient and economical. This needed system must decrease down time. This needed system must efficiently clean the sensor area to reduce the effects of particulate and fluid build-up. This needed system is lacking in the prior art.